a sole employee of a c-corp. what is the most he can contribute? 25% of his comp from the corp? and deferrals of 100% of comp up to 15k for 2006?

In most cases, it will be the lesser of 25% of comp or $44,000. Can't remember if elective deferrals reduce comp in a SEP; I think they do. If it's a SARSEP (one that existed prior to 1997), then the limit is potentially increased for catch up contributions.

TEFRA would not come into play here would it, since said owner/employee is technically not self employed?

Bear in mind that for employee of the Corporation, only W-2 wages are generally considered for plan contribution purposes..

The most that can be deducted AND excluded from the participant's income cannot exceed 25% of taxable compensation (excluding elective other than catch-up deferrals) or $44,000 (plus catch-up contributions of up to $5,000) for 2006. The deductible limit could be higher (because elective deferrals do not reduce compensation upon which the 25% deduction limit is computed). Hope this helps.